Wireless communication systems divide areas of coverage into cells, each of which has traditionally been served by a base station. The base stations support wireless communications with mobile stations. The coverage area provided by a given base station is generally referred to as a cell. As the mobile stations move from one cell to another, the communication sessions are transferred from one base station to another. Unfortunately, the coverage area for a base station can be limited and may vary based on geography and structures located within the coverage area.
In an effort to increase or improve the coverage area provided by base stations, relay stations have been introduced. Relay stations are associated with a given base station and act as liaisons between the mobile stations within the coverage area of the relay stations and the base station. For downlink communications, data may be transmitted from the base station to a relay station and from the relay station to the mobile station. For uplink communications, data may be transmitted from the mobile station to a relay station and from the relay station to the base station. As such, the uplink or downlink path may have multiple hops. Further, multiple relay stations may be provided in the uplink or downlink path. Even when relay stations are employed, mobile stations and base stations may also communicate directly, if the mobile stations are within communication range of the base stations.
As the demand for high speed broadband networking over wireless communication networks increases, so too does the demand for different types of networks that can accommodate high speed wireless networking. For example, the deployment of IEEE 802.11-based wireless networks in homes and business to create Internet access “hot spots” has become prevalent in today's society. However, these IEEE 802.11-based wireless networks are relatively limited in bandwidth as well as communication distance. Thus, these IEEE 802.11-based wireless networks are not good candidates for cellular implementations to provide continuous coverage over extended areas.
In an effort to increase bandwidth and communication distance for longer range wireless networking, the family of IEEE 802.16 standards was developed for next generation wireless communications systems that are cellular based. The IEEE 802.16 standards are often referred to as WiMAX, and provide a specification for fixed broadband wireless metropolitan access networks (MANs) that use a point-to-multipoint architecture. Such communications can be implemented, for example, using orthogonal frequency division multiplexing (OFDM) communication. OFDM communication uses a spread spectrum technique to distribute the data over a large number of carriers that are spaced apart at precise frequencies.
The IEEE 802.16 standards support high bit rates in both uplink and downlink communications up to a distance of about 30 miles (˜50 km) to handle such services as Voice over Internet Protocol (VoIP), IP connectivity and other voice, media, and data applications. Expected data throughput for a typical WiMAX network is 45 MBits/sec. per channel. IEEE 802.16 networks, such as IEEE 802.16j, networks, can be deployed as multi-hop networks, which employ relay stations to act as liaisons between base stations and mobile stations and further extend the effective coverage areas of the associated base stations.
For multi-hop networks, including those employing the IEEE 802.16 standards, there is a need for efficient and effective techniques to provide various ranging functions, channel quality reporting functions, and retransmission control functions when the mobile stations are being served by relay stations. These functions are often critical to enabling effective communications. For example, initial and periodic ranging functions help ensure that mobile stations transmit at the appropriate time and power on the right frequency. The channel quality reporting function helps a mobile station identify and select an appropriate base station or relay station with which to anchor while the retransmission control function ensures that lost data is retransmitted as necessary. Currently, these functions are controlled primarily by the base station that is associated with the relay stations, and the resources of the group are often used inefficiently and performance is degraded.